Manufacture of phosphine



March 26, 1968 M. GQ PALMER MANUFCTURE OF PHOSPHINE United States PatentO 3,375,074 MANUFACTURE F PHOSPHINE Malcolm George Palmer, Lakedown, near Kidderminster,

England, assignor to Hooker Chemical Corporation, v

s claims. (ci. 23-204) This invention consists in a process for the manufacture of phosphine which comprises bringing white phosphorus into contact with an amalgam of mercury with zinc or cadmium in an acid aqueous medium.

While the invention may be carried out with an amalgam of zinc or cadmium, zinc amalgam is preferred and gives an excellent yield of phosphine. The proportion of zinc or cadmium in the amalgam may be high. e.g., up to 70% in the case of zinc but amalgams containing a relatively small proportion of zinc or cadmium are preferred, such as, for example, less than 5%.

To produce the acid medium, any acid may be used which, under the conditions of the reaction, does not signiticantly react with either phosphorus or phosphine. Suitable acids are, for example, sulphuric, acetic, hydrochloric, phosphorus or phosphoric acid. The concentration of the acid in the aqueous medium is not critical, but the more concentrated the acid, the faster the reaction. The reaction will proceed at a pH as high as 5, to which-concentration the acid may be allowed to fall during the course of the reaction. It is, however, preferred to use, .at all events initially, a considerably higher concentration in the range l to moles per litre. The optimum concentration of acid in any particular case depends on the solubility of the reaction products, the composition of ,the amalgam and the specific gravity of the acid. The

relevance of this last factor is due to the fact that it iS usually desirable for the specific gravity of the acid medium to be less than that of the white phosphorus in order Vthat the latter may sink to the level of the amalgam, although in,one process hereinafter described, lthe reverse relationship is required.l l p The reaction takes place at the interface of the amalgam, phosphorus and acid. `It is advantageous to arrange that the phosphorus is present in avthin layer on the surface of the amalgarrijThs may be brought about in one of two ways: The phosphorus may be introduced into the acid a drop at a time as it is consumedJE-ach' drop ysinks until it reaches the `surface of the amalgam wherel upon it spreads in a thin layer over the surface by sur- `-face tension. Alternatively the reaction may be carried out in a tower containing the acid medium which is of suicient specific gravity to enable a layer of white phosphorus to float upon it. The amalgam is allowed to fall, a drop at a time, through the phosphorus, where it picks up a layer of phosphorus so that the reaction takes place' terface mobile, but the stirring should not be 'so vigor# ous as to disperse the amalgam throughout the acid. Such a dispersion in the presence of phosphorusl takes the form of a black emulsion which is only slightly reactive. Retluxing and stirring are not applicable to the tower process described above.

As the phosphine is evolved, the zinc or cadmium is dissolved in the acid medium. Thel metal content of the amalgam may be replenished either by replacing the mercury or depleted amalgam with fresh amalgam separately prepared, or by addition of the other metal to the mercury or depleted amalgam within the reaction vessel during or following the reaction. Thus, for example, zinc in granulatedy or lump form may be dropped through the acid into the mercury or depleted amalgam. These lumps float on the surface of the mercury but are prevented from coming into contact with the acid by a layer of mercury which spreads over the exposed surface of the lump by surface tension.

If desired, the metal may be recovered from the solution, for example by electrolysis. It is convenientl to use a mercury cathode, so that the amalgam may be reconstit'uted.v By this means the process can be operated continuously. Thus, mercury is withdrawn from the reaction vessel as it is formed (i.e. as the zinc or cadmium is used up) and is conveyed to an electrolytic cell in which it forms the cathode. The aqueous medium is also withdrawn from the Vessel at the appropriate rate and is caused to ilow into the cell to form the electrolyte. The mercury flows through the cell, for example over an inert supporting member, and leaves the cell in the form of an amalgam with the metal deposited from the electrolyte. This amalgam is conveyed back to the reaction vessel.

Apparatus for carrying out the invention as a semicontinuous process is described by way of example with reference to the accompanying drawing.

In the drawing, 1 represents the reaction vessel and 2 the electrolysis vessel. These vessels are connected by flexible tubes 3 and 4, the tube 4 connecting their lower ends and the tube 3 being connected with rigid tubes 5 and 6 to form a Siphon. The tube 5 is provided with a control valve 7. The vessel 1 has a further connection 8 controlled by a valve 9, a dropping funnel 10 and an outlet pipe 11 surrounded by a water condenser 12. Each vessel has a stirrer 13 and -14 respectively, and vessel 1 has an electric heater 15 and vessel 2 a cooling coil 16. Vessel 2 has a spiral platinum anode 19 and a Wire cathode connection 20.

To commence operation, vessel 2 is held at a higher level than vessel 1 as shown in the drawing, the means for holding and adjusting the heights of the vessels not, however, being shown. The amalgam is poured into the vessel 2 and ilows through tube 4 into vessel 1, as shown at 17. Vessel 1 is then purged with an inert gas. The acid medium is then poured into vessel 2, a suction pump is connected with tube 8, the valves 7 and 9 are opened and the outlet 11 is momentarily closed. Acid is drawn into the siphon 6, 5, 3 and then siphons over into vessel 1, the valve 9 being meanwhile closed. When the siphoning is completed, the valve 7 is closed. White phosphorus in the dropping funnel 10 is kept molten by a heater (not shown) and is allowed to fall dropwise into the acid. The acid is maintained at reuxing temperature, and gas containing phosphine is evolved through outlet 11.

When the output of phosphine has dropped to a predetermined rate, the vessel 2 is lowered so that the depleted amalgam flows into it through tube 4. The siphon is filled by connecting nitrogen under pressure to connection 8, valves 7 and 9 being now opened, and outlet 11 being momentarily closed. When the acid has siphoned over into the vessel 2, a positive potential is applied to anode 19 and a negative potential to cathode connection 20 which is now covered by the amalgam. Electrolysis is carried out at '200 milliamps per cm.2 until hydrogen begins to be evolved at the cathode, whereupon the vessel 2 is again raised and the cycle of operations recommenced.

EXAMPLES 1-4 An amalgam was prepared by bringing together zinc and mercury under 50 mls. distilled water while reiiuxing. said reacting taking place at an interface of said aqueous 100 mls. of acid were then added, followed by white phos- .solution of an acid, vamalgam and white phosphorus, said phorus. The mixture was maintained under reflux and aqueous solution of an acid having a specific gravity we ll stirred, and a gas consisting of a mixture of phosgreater than that of said white phosphorus, and in which phine and hydrogen evolved. said reacting includes iioating said white phosphorus on TABLE I Example 1 2 3 4 Metal and quantity zinc, s.4os4 zinc, 3.i3s0 Zine, a.29o2 Zinc, 3.5067. Quantity of mercury (gms.). 64. 892 64.5986 3701 6 .4282. Acid and concentration (molar) HaPOi, 6M H2304, 3M. Quantity (gms.) of phosphorus P4 69 0.9 0.997. Quantity of PHa and H2 evolved (litres) 0.792 0.737 0.854 0.798. Percentage PH3 95 94 85 97.

EXAMPLES 5-7 said aqueous solution of an acid, and dropping said amalgain, a drop at a time, thru the layer of white phosphorus,

whereby it picks up a layer of phosphorus so that the reacting occurs as said drop falls thru said aqueous solution of acid.

4. A process in accordance With claim 3 wherein the id is selected from the group consisting of sulphuric,

acetic, hydrochloric, phosphorous and phosphoric acids,

An amalgam was prepared by electrolysing a solution of zinc sulphate or cadmium sulphate in mls. distilled water with a mercury cathode. Electrolysis was carried out until all the zinc or cadmium ions had been removed from solution. The amalgam was then washed and added 2O to mls. of distilled water. The water was heated under ac reflux and then l0() mls. of acid were added, followed by phosphorus, The mixture was maintained under reux wherein the concentration of the acid in the aqueous and well stirred, and a gas consisting of a mixture of medium S in the fange 0f 1 '0 10 H1015 Per ll'fef and pohsphine and hydrogen was evolved. wherein the reaction is conducted at reflux.

TABLE II Example 5 6 7 Metsi sait and quantity (gms.) znsotrrno, 51 3 znsoif/Hio, 59.9-.- 3CdS04.8H=0. 33.4- Weight 0i mercury cathode (gms.) 1.6760 132.3812 132.8252. Acid and concentration (molar)- Acetic. acid, 3.5M HC1, 6M. Quantity (gms.) o phosphorus P4 2 7.

Quantity of PH3 and Hi evolved (litres) Percentage PHa 96 20 In the case of Example 6, traces of solid hydrides 5. An apparatus for the preparation of phosphine cornequivalent to 10 mgms. of P4 were deposited on the walls 3f prising (1) a reaction vessel, (2) an electrolytic cell 1 n of the apparatus. o which a depleted amalgam is a cathode of said electrolytic EXAMPLE 8 cell, (3) a conduit means including at least two separate conduits comprising a first tiexible conduit and a second 57685 gms. 0f granulated zinc was added to 473.3 exible conduit, said first conduit being connected to subgms. of mercury in 224 mls. of reiixing 6 molar ortho- 40, stantially a lower part of each of said reaction vessel. and phosphoric acid in the PreSeHCe 0f 2.3 gms. 0f White .said electrolytic cell, said second conduit being connected phosphorus, the medium being well stirred. The area of to said' electrolytic cell and to a substantially upper part the mercury Surface When Static WHS 44 111.2- A gas 00nof said reaction vessel, said second conduit further intaining 99,5% 0f PhOSPhD@ 011 a dry Weight/101111116 baSS cluding a valve means `associated therewith, whereby it was evolved. 4- can function as a siphon, (4) a means for electrolyzing What I Claim SI o lsaid electrolytic cell, and (5) a means for adding white 1- A PFOCGSS OF Preparing PhOSPhUe Comprising fe phosphorus to said reaction vessel. acting white phosphorus, an amalgam of mercury and a metal selected from the group consisting of zincr and cad- A References Cited mium, andl a corrposition consisting essentially of an 50 UNITED STATES PATENTSv aqueous so ution o an acid at a pH ranging up to pH 5, said reacting taking place at an interface of said aqueous 2938771 5/1960 Avdlklan 23-116 solution of acid, white phosphorus and amalgam which i 11712352 5/1929 Crelghton f 204- 220 forms a layer beneath said aqueous solution of acid, said 21876192 3/1959 Wurbs aqueous solution of acid further having a speciiic gravity 55 219521604 9/1960 De Nora 23 204 less than that of said white phosphorus, and in which said 2,469,879 '5/1949 Hurd reacting includes dropping said white phosphorus, a drop 3,019,087 1/1962 Jacob et al.\ 23-204 at a time, through said aqueous solution of acid, whereby FOREIGN PATENTS it drops to the bottom of said aqueous solution of acid and reaches the surface of the amalgam and forms a thin 776629 6/1957 Great Bmvam' layer thereon. y OTHER REFERENCES 2. A process in accordance with claim 1, wherein the :GmelnkKmun Handbuch der Anorganischen Chemie, acid is selected from the group consisting of sulphun'c, 7th editiom 191L v01. L part 1H, n 64 acetic, hydrochloric, phosphorous and phosphoric acids, Pascal, Noveau Tria De Chimie Minerale, 195.8, wherein the concentration of the acid in the aqueous '65, VOLXI pp 550 551 medium is in the range of 1 to 10I moles per liter, and Mener, 'Comprehensive Treatise on Inorganic and wherein the reaction is conducted at reflux. Theoreticl Chemistry ,v'01 8 pp. 806, 813 (192g),

3. A process for preparing phosphine comprising reacting white phosphorus, an amalgam of ymercury and a MILTON WEISSMAN, Primary Examiner. metal selected from the group consisting of zinc and cadmiurn, yand a composition consisting essentially Aof an mf MAURICE A' BRINDISI Examiner aqueous solution of an acid .at a pH ranging up to pH 5, M, N, MELLER, R, DAVIDSOlI, Assistant Examiners. 

1. A PROCESS FOR PREPARING PHOSPHINE COMPRISING REACTING WHITE PHOSPHORUS, AS AMALGAM OF MERCURY AND A METAL SELECTED FROM THE GROUP CONSISTING OF ZINC AND CADMIUM, AND A COMPOSITION CONSISTING ESSENTIALLY OF AN AQUEOOUS SOLUTION OF AN ACID AT A PH RANGING UP TO PH5, SAID REACTING TAKING PLACE AT AN INTERFACE OF SAID AQUEOUS SOLUTION OF ACID, WHITE PHOSPHORUS ANDAMALGAM WHICH FORMS A LAYER BENEATH SAID AQUEOUS SOLUTION OF ACID, SAID AQUEOUS SOLUTION OF ACID FURTHER HAVING A SPECIFIC GRAVITY LESS THAN THAT OF SAID WHITE PHOSPHORUS, AND IN WHITE SAID REACTING INCLUDES DROPPING SAID WHITE PHOSPHORUS, A DROP AT A TIME, THROUGH SAID AQUEOUS SOLUTION OF ACID, WHEREBY IT DROPS TO THE BOTTOM OF SAID AQUEOUS SOLUTION OF ACID AND REACHES THE SURFACE OF THE AMALGAM AND FORMS A THIN LAYER THEREON. 